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71.
Katarina EA Nostell Birgitta Essén-Gustavsson Johan T Bröjer 《Acta veterinaria Scandinavica》2012,54(1):7
Background
The branched chain amino acid leucine is a potent stimulator of insulin secretion. Used in combination with glucose it can increase the insulin response and the post exercise re-synthesis of glycogen in man. Decreased plasma amino acid concentrations have been reported after intravenous or per oral administration of leucine in man as well as after a single per oral dose in horses. In man, a negative correlation between the insulin response and the concentrations of isoleucine, valine and methionine have been shown but results from horses are lacking. This study aims to determine the effect of repeated per oral administration with a mixture of glucose and leucine on the free amino acid profile and the insulin response in horses after glycogen-depleting exercise. 相似文献72.
73.
A model of the carbohydrate recognition domain CRD, residues 111-245, of
hamster galectin-3 has been made using homology modeling and dynamics
minimization methods. The model is based on the known x-ray structures of
bovine galectin-1 and human galectin-2. The oligosaccharides
NeuNAc-alpha2,3-Gal-beta1,4-Glc and GalNAc-alpha1, 3-
[Fuc-alpha1,2]-Gal-beta1,4-Glc, known to be specific high-affinity ligands
for galectin-3, as well as lactose recognized by all galectins were docked
in the galectin-3 CRD model structure and a minimized binding conformation
found in each case. These studies indicate a putative extended
carbohydrate-binding subsite in the hamster galectin- 3 involving Arg139,
Glu230, and Ser232 for NeuNAc-alpha2,3-; Arg139 and Glu160 for
fucose-alpha1,2-; and Arg139 and Ile141 for GalNAc-alpha1,3- substituents
on the primary galactose. Each of these positions is variable within the
whole galectin family. Two of these residues, Arg139 and Ser232, were
selected for mutagenesis to probe their importance in this newly identified
putative subsite. Residue 139 adopts main-chain dihedral angles
characteristic of an isolated bridge structural feature, while residue 232
is the C-terminal residue of beta- strand-11, and is followed immediately
by an inverse gamma-turn. A systematic series of mutant proteins have been
prepared to represent the residue variation present in the aligned
sequences of galectins-1, - 2, and -3. Minimized docked models were
generated for each mutant in complex with NeuNAc-alpha2,3-Gal-beta1,4-Glc,
GalNAc-alpha1, 3-[Fuc- alpha1,2]-Gal-beta1,4- Glc, and Gal-beta1,4-Glc.
Correlation of the computed protein-carbohydrate interaction energies for
each lectin- oligosaccharide pair with the experimentally determined
binding affinities for fetuin and asialofetuin or the relative potencies of
lactose and sialyllactose in inhibiting binding to asiolofetuin is
consistent with the postulated key importance of Arg139 in recognition of
the extended sialylated ligand.
相似文献
74.
Nucleotide sequence analysis of the human salivary protein genes HIS1 and HIS2, and evolution of the STATH/HIS gene family 总被引:1,自引:0,他引:1
Human histatins are a family of low-M(r), neutral to very basic,
histidine-rich salivary polypeptides. They probably function as part of the
nonimmune host defense system in the oral cavity. A 39-kb region of DNA
containing the HIS1 and HIS2 genes was isolated from two human genomic
phage libraries as a series of overlapping clones. The nucleotide sequences
of the HIS1 gene and part of the HIS2(1) gene were determined. The
transcribed region of HIS1 spans 8.5 kb and contains six exons and five
introns. The HIS1 and HIS2(1) genes exhibit 89% overall sequence identity,
with exon sequences exhibiting 95% identity. The two loci probably arose by
a gene duplication event approximately 15-30 Mya. The HIS1 sequence data
were also compared with that of STATH. Human statherin is a low-M(r) acidic
phosphoprotein that acts as an inhibitor of precipitation of calcium
phosphate salts in the oral cavity. The HIS1 and STATH genes show nearly
identical overall gene structures. The HIS1 and STATH loci exhibit 77%-81%
sequence identity in intron DNA and 80%-88% sequence identity in noncoding
exons but only 38%-43% sequence identity in the protein-coding regions of
exons 4 and 5. These unusual data suggest that HIS1, HIS2, and STATH belong
to a single gene family exhibiting accelerated evolution between the HIS
and STATH coding sequences.
相似文献
75.
Evolution of the Adh locus in the Drosophila willistoni group: the loss of an intron, and shift in codon usage 总被引:1,自引:0,他引:1
We report here the DNA sequence of the alcohol dehydrogenase gene (Adh)
cloned from Drosophila willistoni. The three major findings are as follows:
(1) Relative to all other Adh genes known from Drosophila, D. willistoni
Adh has the last intron precisely deleted; PCR directly from total genomic
DNA indicates that the deletion exists in all members of the willistoni
group but not in any other group, including the closely related saltans
group. Otherwise the structure and predicted protein are very similar to
those of other species. (2) There is a significant shift in codon usage,
especially compared with that in D. melanogaster Adh. The most striking
shift is from C to U in the wobble position (both third and first
position). Unlike the codon-usage-bias pattern typical of highly biased
genes in D. melanogaster, including Adh, D. willistoni has nearly 50% G + C
in the third position. (3) The phylogenetic information provided by this
new sequence is in agreement with almost all other molecular and
morphological data, in placing the obscura group closer to the melanogaster
group, with the willistoni group farther distant but still clearly within
the subgenus Sophophora.
相似文献
76.
An exception to the generally conservative nature of plastid gene evolution
is the gene coding for the beta" subunit of RNA polymerase, rpoC2. Previous
work by others has shown that maize and rice have an insertion in the
coding region of rpoC2, relative to spinach and tobacco. To assess the
distribution of this extra coding sequence, we surveyed a broad
phylogenetic sample comprising 55 species from 17 angiosperm families by
using Southern hybridization. The extra coding sequence is restricted to
the grasses (Poaceae). DNA sequence analysis of 11 species from all five
subfamilies within the grass family demonstrates that the extra sequence in
the coding region of rpoC2 is a repetitive array that exhibits more than a
twofold increase in nucleotide substitution, as well as a large number of
insertion/deletion events, relative to the adjacent flanking sequences. The
structure of the array suggests that slipped-strand mispairing causes the
repeated motifs and adds to the mechanisms through which the coding
sequence of plastid genes are known to evolve. Phylogenetic analyses based
on the sequence data from grass species support several relationships
previously suggested by morphological work, but they are ambiguous about
broad relationships within the family.
相似文献
77.
Background
The Burkholderia cepacia complex (Bcc) is a collection of nine genotypically distinct but phenotypically similar species. They show wide ecological diversity and include species that are used for promoting plant growth and bio-control as well species that are opportunistic pathogens of vulnerable patients. Over recent years the Bcc have emerged as problematic pathogens of the CF lung. Pseudomonas aeruginosa is another important CF pathogen. It is able to synthesise hydrogen cyanide (HCN), a potent inhibitor of cellular respiration. We have recently shown that HCN production by P. aeruginosa may have a role in CF pathogenesis. This paper describes an investigation of the ability of bacteria of the Bcc to make HCN. 相似文献78.
Interactions between charged amino acid residues within transmembrane helices in the sulfate transporter SHST1 总被引:2,自引:0,他引:2
The aim of this study was to identify charged amino acid residues important for activity of the sulfate transporter SHST1. We mutated 10 charged amino acids in or near proposed transmembrane helices and expressed the resulting mutants in a sulfate transport-deficient yeast strain. Mutations affecting four residues resulted in a complete loss of sulfate transport; these residues were D107 and D122 in helix 1 and R354 and E366 in helix 8. All other mutants showed some reduction in transport activity. The E366Q mutant was unusual in that expression of the mutant protein was toxic to yeast cells. The R354Q mutant showed reduced trafficking to the plasma membrane, indicating that the protein was misfolded. However, transporter function (to a low level) and wild-type trafficking could be recovered by combining the R354Q mutation with either the E175Q or E270Q mutations. This suggested that R354 interacts with both E175 and E270. The triple mutant E175Q/E270Q/R354Q retained only marginal sulfate transport activity but was trafficked at wild-type levels, suggesting that a charge network between these three residues may be involved in the transport pathway, rather than in folding. D107 was also found to be essential for the ion transport pathway and may form a charge pair with R154, both of which are highly conserved. The information obtained on interactions between charged residues provides the first evidence for the possible spatial arrangement of transmembrane helices within any member of this transporter family. This information is used to develop a model for SHST1 tertiary structure. 相似文献
79.
The apoptotic ligands TRAIL,TWEAK, and Fas ligand mediate monocyte death induced by autologous lupus T cells 总被引:14,自引:0,他引:14
Kaplan MJ Lewis EE Shelden EA Somers E Pavlic R McCune WJ Richardson BC 《Journal of immunology (Baltimore, Md. : 1950)》2002,169(10):6020-6029
Individuals with systemic lupus erythematosus show evidence of a significant increase in monocyte apoptosis. This process is mediated, at least in part, by an autoreactive T cell subset that kills autologous monocytes in the absence of nominal Ag. We have investigated the apoptotic pathways involved in this T cell-mediated process. Expression of the apoptotic ligands TRAIL, TNF-like weak inducer of apoptosis (TWEAK), and Fas ligand on lupus T cells was determined, and the role of these molecules in the monocyte apoptotic response was examined. We report that these apoptotic ligands mediate the autologous monocyte death induced by lupus T cells and that this cytotoxicity is associated with increased expression of these molecules on activated T cells, rather than with an increased susceptibility of lupus monocytes to apoptosis induced by these ligands. These results define novel mechanisms that contribute to increased monocyte apoptosis characterizing patients with lupus. We propose that this mechanism could provide a source of potentially antigenic material for the autoimmune response and interfere with normal clearing mechanisms. 相似文献
80.
We have cloned and characterized the first member of a novel family of ammonium transporters in plants: AtAMT2 from Arabidopsis thaliana. AtAMT2 is more closely related to bacterial ammonium transporters than to plant transporters of the AMT1 family. The protein was expressed and functionally characterized in yeast. AtAMT2 transported ammonium in an energy-dependent manner. In contrast to transporters of the AMT1 family, however, AtAMT2 did not transport the ammonium analogue, methylammonium. AtAMT2 was expressed more highly in shoots than roots and was subject to nitrogen regulation. 相似文献